The present invention relates to a xe2x80x9cdryxe2x80x9d brake pedal system. One aspect of the invention relates to a device that emulates a conventional vacuum or hydraulic brake pedal system wherein a non-linear brake pedal travel versus brake pedal force characteristic is achieved with simultaneous dynamic dampening.
Vehicle drivers have become accustomed to the xe2x80x9cfeelxe2x80x9d of a brake pedal resistance that mirrors a manually applied braking force. Braking systems commonly known as brake-by-wire (BBW) or similar systems typically include a master cylinder that is isolated from the braking system. Such BBW systems rely on automatic electric or electric-hydraulic means to remotely activate the brake. Consequently, brake pedal xe2x80x9cfeelxe2x80x9d can be different to that during a manual application of the braking force. This has provided an impetus to develop a brake pedal actuator that has the xe2x80x9cfeelxe2x80x9d of a resistance force coacting against the driver in a manner normally provided by manual apply systems.
The limited space under an automobile instrument panel calls for a compact brake system. Hydraulic fluid braking systems are compact, but are costly and can be prone to failure due to temperature sensitivity and need for efficient sealing. Alternatively, xe2x80x9cdryxe2x80x9d BBW systems do not require pressurized hydraulic fluid, but are generally bulky due to the need for additional components to emulate xe2x80x9cfeelxe2x80x9d. For example, external dampers are useful for emulating xe2x80x9cfeelxe2x80x9d, but also increase unit size. Current innovations have lead to either increased unit cost or a discernable difference in the brake pedal xe2x80x9cfeelxe2x80x9d characteristic during brake application.
Therefore, it would be desirable to achieve a xe2x80x9cdryxe2x80x9d BBW system that is reliable, compact, relatively inexpensive to manufacture, and capable of emulating the xe2x80x9cfeelxe2x80x9d of a conventional vacuum or hydraulic brake pedal system.
One aspect of the invention provides a brake pedal emulator system comprising an emulator housing, a damper positioned within and operably attached to the emulator housing, a shaft that is slidably received within the emulator housing, and a sequential spring system positioned within the emulator housing and in operable contact with the shaft. The shaft compresses the sequential spring system while the damper exerts a dynamic dampening force against the movement of the shaft. The shaft is comprised of a clevis, a damper housing, and a shaft bar that is attached at a first end to said clevis and at a second end to said damper housing. The damper is comprised of: a damper rod that is positioned within and retained by the emulator housing, a damper piston that is attached to a first end of said damper rod, and a damper housing which is attached at a first end to the shaft bar, terminates at a second end into a shoulder structure, and encompasses the damper rod. An orifice is formed between the damper piston and the damper housing that allows a fluid to flow from a damper reservoir to a variable chamber. This embodiment of the invention further provides for the sequential spring system to be comprised of a plurality of springs wherein said springs are each fabricated of steel coil. Furthermore, the plurality of springs is comprised of a first, second, third, and fourth spring positioned within the emulator housing. The first spring is positioned between a first end of the emulator housing and a flange portion of the shaft, the second spring is positioned between the shoulder structure of the damper housing and a floating washer, the third spring is position between said washer and a septum portion of the emulator housing, and the fourth spring is positioned coaxially with the third spring. The first, third, and fourth springs are positioned coaxially with respect to the shaft. Finally, a force transducer and a travel transducer are positioned within the emulator housing and operably attached to the shaft in order to measure brake pedal force and shaft travel, respectively.
Another aspect of the invention provides for an application of a brake pedal force which results in transmission of said force to a shaft that is slidably received by an emulator housing. A plurality of springs positioned with the emulator housing is sequentially compressed while a dampening member positioned within said emulator housing generates a dynamic dampening force against the shaft. Internally positioned transducers measure brake pedal force and shaft travel and output signals proportional to said force and said travel are relayed to activate a brake. During operation, a reaction force is generated by the brake pedal emulator system at a brake pedal that is operably attached to the shaft. The reaction force is comprised of a combination of the dampening force and a spring force wherein the spring force increases with a sequential compression of the plurality of springs. The sequential compression of springs is comprised of a serial and a parallel compression of two or more springs. Furthermore, an order of the sequential compression of the plurality of springs is determined by a free travel distance of each spring.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.